1. Field of the Invention
The ability to prepare estriol compounds from simple intermediates provides many advantages. First, it avoids the dependence on natural products, which are subject to fluctuations in availability and economics. Secondly, complete synthesis frequently provides greater flexibility for the introduction of functionalities at various sites in the molecule. Finally, complete synthesis frequently provides greater overall yields than can be obtained from naturally occurring molecules, which may require extensive modification.
2. Description of the Prior Art
Johnson, Accounts of Chemical Research, page 1, January 1968, describes nonenzymic biogenetic-like olefinic cyclizations using aliphatic compounds. Johnson, et al., J. Am. Chem. Soc. 93 4332 (1971) discloses cyclizations of aliphatic compounds to steroidal structures employing an alkinyl terminating group. See also Abrams, et al., Bio-organic Chemistry, 1, 243 (1971).